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<body><span class="vcard"><a class="email" href="mailto:dark_sylinc@yahoo.com.ar" title="Matias N. Goldberg <dark_sylinc@yahoo.com.ar>"> <span class="fn">Matias N. Goldberg</span></a>
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<a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - GL_ARB_buffer_storage crippled extension on r600, radeonsi and amdgpu Mesa drivers"
href="https://bugs.freedesktop.org/show_bug.cgi?id=102204">bug 102204</a>
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<td>dark_sylinc@yahoo.com.ar
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<b><a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - GL_ARB_buffer_storage crippled extension on r600, radeonsi and amdgpu Mesa drivers"
href="https://bugs.freedesktop.org/show_bug.cgi?id=102204#c10">Comment # 10</a>
on <a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - GL_ARB_buffer_storage crippled extension on r600, radeonsi and amdgpu Mesa drivers"
href="https://bugs.freedesktop.org/show_bug.cgi?id=102204">bug 102204</a>
from <span class="vcard"><a class="email" href="mailto:dark_sylinc@yahoo.com.ar" title="Matias N. Goldberg <dark_sylinc@yahoo.com.ar>"> <span class="fn">Matias N. Goldberg</span></a>
</span></b>
<pre>OK this left me wondering.
I looked further into what happens when you call glBufferStorage, and it seems
that buffer_usage in st_cb_bufferobjects.c
<a href="https://github.com/anholt/mesa/blob/master/src/mesa/state_tracker/st_cb_bufferobjects.c#L226">https://github.com/anholt/mesa/blob/master/src/mesa/state_tracker/st_cb_bufferobjects.c#L226</a>
stores all buffers in VRAM unless GL_CLIENT_STORAGE_BIT is used because it
always returns PIPE_USAGE_DEFAULT.
The chosen pipe_resource_usage will end up in si_init_resource_fields
(<a href="https://github.com/anholt/mesa/blob/master/src/gallium/drivers/radeonsi/si_buffer.c#L103">https://github.com/anholt/mesa/blob/master/src/gallium/drivers/radeonsi/si_buffer.c#L103</a>)
which ends up putting the buffers all buffers in VRAM with Write Combining
(unless GL_CLIENT_STORAGE_BIT is set)
That is... an odd choice. This is specially bad for buffers requested with
GL_MAP_READ_BIT flags, which clearly should not be stored in VRAM with WC bits
set.
This indeed looks like a bug to me. Unfortunately, these hint flags don't map
really well to HW.</pre>
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